Electrooptical image production



' oct. 27, 1936. R. c. MATHES 2,058,898

ELEGTROOPTI CAL IMAGE PRODUCTION Tram/ff Oct. 27, 1936. R. c. MA1-HES ELECTROOPTICAL IMAGE PRODUCTION Filed Nov. 12, 1927 2 Sheets-Sheet 2 Patented Oct. 27, 1936 PATENT oFFlcE ELECTROOPTICAL IMAGE PRODUCTION Robert C. Mathes, Wyoming, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 12, 1927, serial n1232551 16 Claims. (Cl. 1713-6) This invention relates to electro-optical image production and particularly to a method and means for increasing the brightness of images of the kind produced by television systems.

In a copending application of F. Gray, Serial No. 181,538, filed April 6, 1927, there is disclosed a system which has been used successful- 1y for producing images electro-optically. In this system there isV employed at the receiving station a bank of light emitting elements which are actuated periodically in succession by current impulses corresponding to instantaneous aspects of elemental areas of the object or eld being scanned at the transmitting station, thereby setting up lig-ht impulses of short duration. These light impulses occur in rapid succession in order to give the eye of the observer the impression of seeing a complete image. Be-

cause of the short duration of each light impulse the apparent brightness of the image is relatively small. f

In accordance with the present invention the light emitting or controlling elements of the image producing apparatus are periodically actuated in succession in accordance with instantaneous aspects of corresponding elemental areas of an object or eld being scanned and are maintained actuated ln accordance with a given aspect of the corresponding elemental area of the object or field while succeeding actuations of4 other elements take place, and -preferably until the scanning cycle has been completed. The image produced in this manner appears considerably brighter than the image producedA by the method in which only one element is in the actuated state at one time. y

In one of the specific embodiments of the invention hereinshown and described, a commutator driven in phase with the scanning means is employed for connecting condensers one at a time' and periodically to a source of potential which varies in accordance with the variations inshade 'of the elemental areas of the field being scanned. Each condenser is connected to the input circuit of a voltage controlled repeater of the vacuum tube type for varying the amplitude of the current iiowing in a transmission channel associated with the output circuit of the repeater. At the receiving station each of the transmission channels is associated with image producing apparatus' including one of a bank of light controlling or light producing elements ksuch as an incandescent lamp. It is thus seen that light emitted by each of these elements is of an intensity vwhich corresponds to the charge on one of the condensers, which in turn is in accordance with the tone Value of a given aspect of an elemental area of the eld of view and this light is sustained for a considerable period in accordance with this aspect. 5

In another specific embodiment of the invention instead of providing a plurality of transmission channels, one for each of the elemental areas vof the eld of view,the image currents are transmitted over a single channel which is 10 connected to the commutator at the receiving station. This'commutator serves to charge a plurality of condensers in succession and periodically in accordance with instantaneous aspects of elemental areas of the iield scanned at the transmitting'station, and' these condensers control the light produced by the elements of an imageV producing apparatus in a manner as described above.

In addition to increasing the brightness of the image by sustaining the light produced by each element of the image producing apparatus while other elements are being actuated, the advantage of reducing flicker is realized. In a system in which the actuation of the elements is not sustained a light llash occurs each time that an image impulse corresponding to a given elemental area of the object or field ci view is received, while in the system of this invention a light flash occurs only at the element of the image producing apparatus corresponding to the elemental area of the object, the aspect of which is changing.

The invention may be readily understood 'by referring to the following detailed description and the accompanying drawings in which Fig. l is a diagrammatic view of a television system in accordance with the present invention,

Fig. 2 is a diagrammatic view of a modification of the television system shown in Fig. 1, and 40 Fig. 3 isa front elevation of a portion of the bank of light producing elements employed in connection with the systems shown in Figs. 1 and 2.

'Referring now to Fig. 1 -of the drawings the 45 television system shown comprises a transmitting station A and a receiving `station B. At the station A the subject l0 comprising the field of View an image of which is to be produced at the receiving station is located in front of a scanning apparatus. This apparatus comprises an arc lamp II and an optical system for causing a slender pencil of substantially parallel rays of intense light to sweep across the eld in front of the scanning apparatus and scan the subject I0 in a series of successive parallel lines. The optical system includes a scanning disc I2 which has a number of small circular apertures I3 arranged in a spiral extending around the disc near its rim, and which is driven by the motor 20. Light from the arc I I is directed by a lens system I4 so that an intense beam of light passes through each aperture as it moves across the illuminated area of the disc. An opaque screen I5 in front of the disc is provided with a rectangular opening I5 of such width as to emit light from only one aperture of the scanning disc at a time. Lens I1 bends the slender pencil of parallel rays passing through the aperture I3 and the opening I 8 to form an image of the moving aperture on the subject I0. As a result of this arrangement the subject is completely scanned once for each revolution of the disc in a'series of successive parallel lines by a small rapidly moving intensely bright spot of light. As the spot of light passes over the subject light is diffusely reflected therefrom and a. portion ofthe reflected light reaches the photo-sensitive surface of a large aperture photo-electric cell I8 which is connected to the input circuit of a vacuum tube amplier I9. 4This portion of the television system is shown and described in the copending application of F. Gray referred to above.

'I'he output of the amplifier I9 is connected through condenser 2I of large capacity and resistance 22 to ground. The ungrounded terminal of this resistance is also connected to the brush 23 of the rotary distributor 24 which has as many contacts as the number of elemental areas into which the subject I0 is divided for image producing purposes and which distributor is directly coupled to the motor 20 so that' it is driven in synchronism with the scanning disc I2. Each contact of the rotary distributor is connected to a plate of one of a plurality of condensers 25, two of which are shown in the drawings for the purpose of illustration, the remaining plate of each condenser being grounded. Each condenser 25 is shunted by a resistance 26, which may be the leakage resistance of the condenser, and connected to the input terminals of a vacuum tube repeater 21. The output circuit of this repeater is connected to a circuit comprising the condensersA 28 and 29, resistance 30 and the secondary winding 3l of a transformer the primary winding of which is connected to an oscillation generator 32. The transmission medium 33 which connects the transmitting and receiving stations is connected between ground and a mid-terminal of the secondary transformer winding 3|.

As the subject III is scanned, electrical impulses corresponding to the shades of successive elemental areas of the subject are set up by the photo-electrical cell I8. These impulses after being amplified by the amplifier I 9 are impressed across the resistance 22 thus causing corresponding potential differences across the terminals thereof. A potential corresponding to the shade of each elemental area of the subject I0 is then impressed upon one of the condensers 25 which is charged accordingly. 'I'his potential to which each condenser 25 is charged acts in series with a biasing battery 34 of the vacuum tube repeater 21 and causes the output impedance of the repeater to change in accordance with its magnitude. The circuit comprising the output of the repeater 21, condensers 28 and 29, resistance 30 and the secondary winding of transformer 3| is so adjusted that normally none of the current generated by the oscillator 32 flows through the Cil mission medium 33 to the receiving station B.

'I'he oscillators 32 produce currents of different frequency respectively, and each of the band pass lters 35 at the receiving station B are designed lto pass current produced by one of these oscillators to one of the bank of light producing elements 35 which may be small incandescent lamps. The value of resistance 22 and the capacity of the condenser 25 should be such that the condenser is charged within the time that a circuit is completed through each of the contacts of the distributor 24. Satisfactory results may be obtained by making the value of the resistance of the order of 5,000 to 10.000 ohms and the capacity of each condenser of the order of 0.001 microfarad. The value of the resistance 26 should be high, for instance, of the order of megohms s'o that the charge on condenser 25 is not reduced appreciably during the time of a complete scanning of the subject I0. It is thus apparent that the light produced by each of the bank of light producing elements 38 is of an intensity proportional to the shade of a corresponding elemental area of the subject I0 and this light is maintained at a constant value corresponding to a given aspect of the elemental area of the subject I0 until the aspect of this area changes.

The scanning apparatus employed at the transmitting station A of the television system shown in Fig. 2 is the same as that employed in the system shown in Fig. l and the parts are cor# respondingly numbered. The electrical image impulses set up by thephoto-electric cell I8 and amplified by the amplifier I9 are transmitted to the receiving station B over the transmission channel 31 which is connected to the transformers 38 and 39 located at the transmitting and receiving stations respectively.

The incoming image impulses are amplified by the vacuum tube amplifier 40 and are then impressed upon the resistance 4I connected in its output circuit through a condenser 5I of large capacity. This resistance is connected successively to one of the condensers 43 through the contacts of the rotary' distributor 42 which is driven by the motor 52. The motors 20 and 52 are maintained in synchronism by any suitable means represented by the devices 53 and 54 shown connected by the transmission line 55. A system which has been employed successfully for synchronizing the elements at different stations of a television system is disclosed in Patent 1,763,909, granted June 17, 1930 on an application of H. M. Stoller and E. R. Morton, Serial No. 200,799, filed June 23, 1927. The condensers 43 are charged in succession to a potential corresponding to the potential difference measured between the terminals of resistance 4I and therefor in accordance with the shades of successive elemental areas of the subject I0. These condensers are each connected in the input circuit of one of a plurality of repeater elements of the vacuum tube type having a cathode 44, a grid 45 and an anode 46, and one of a bank of light producing elements 36, such as a small incandescent lamp, is connected in the anode circuit of each repeater in series with a source of anode current 48. 'I'he grid 45 of each repeater is normally biased by a battery 49 through a resistance 50 so t1 at the sistance of 5,000 to 10,000 ohms.

y 2,058,898. anode lcurrent is of such a magnitude that thelamps normally appear dark but emitan appreciable amount of light when the anode current is increased slightly. -This increase in anode currentand the consequent emission of light occurs when one of the condensers becomes charged in accordance with an incoming image impulse corresponding to the shade of an elemental area of the object I0. The electromotive force to which the condenser is charged is impressed across the terminals of the 'resistance 50 which may represent the leakage resistance of condenser 43, thus placing a positive electromotive force in series with the negative biasing pulse of different value corresponding to a-dif ferent aspect o f the elemental area of the subject is received. The value of resistance Il and the capacity of condenser 4 3 should preferably be such that the condenser can be charged'in accordance with the received image impulse during the time that the` distributor completes a circuit through each contact. As explained in connection with the system of Fig. 1, satisfactory results can be obtained by employing a condenser having a capacity of 0.001 microfarad and a re- The value of resistance 50 should be suiciently high that the charge on each condenser 43 is not reduced appreciably during the time of a complete scanning of the object I0. A value of the order of L megohms has been found to be satisfactory. Fig. 3 shows in irontelevation a portion ofthe bank of light producing elements i36 which is employed at the receivingstations B of the systems shown in Figs. 1 and 2 for the production of an image of the subject IIJ. Io obtain an image of good `qualitya large number of these elements -in close space relation should be employed, a vbank of 2,500 elements having beenv found to be satisfactory.

It is to be understood that it is within the light ,producing elements other elements which emit energy of a frequency range which extends above or below the visible spectrum.

What is claimedis: 4

f1. In an electro-optical system vior producing images of a field of view. a plurality of condenser elements, means for charging said elements in succession periodically in accordance with tone values of elemental areas of said eld of view, a plurality of voltage controlled repeaters associated conductively with said condenser elements respectively, and means controlled by said repeaters-for producing an image of said eld of view. y

2. In an electro-optical system for producing images of a eld of view, means for scanning elementalareas of said field in succession, a source of potential, means for varying the amplitude of potential, a voltage controlled repeating device, and means for continuously conductively associating said repeating device with said condenser.

3. Inv an electro-optical system for producingimages of a field of view. means for scanning elemental areas of said field in succession, a source -of potential, means for varying the amplitude of said potential in accordance with the tone values of successively scanned elemental areas, a Y

'plurality of condensers, means for successively associating said condensers with said source of potential, a plurality of voltage controlled repeating devices, one for each'of said condensers,

means for conductively associating said repeating devices with said' condensers, respectively, image producing apparatus at a distant station, and

means for transmitting energy controlled by said repeating devices to said station to control the production of the image.

4. Inan electro-optical system for producing images of a field oi view, a transmitting station and a receiving station, means at said transmitting station forsetting up image current impulses corresponding to the shade of successive elemental plane, means embodying a gaseous lamp for' transiently exciting' illumination of `said picture plane in elementary areas, and means including a condenser and a resistance in circuit with the gaseous lamp for securing persistence of illumination of saidl elementary areas for a time approximatelyequal to persistence of vision of the human eye. 6. In receiving apparatus for televisionsystems, fthe combination of a relay operated by the received signals, an electric lamp arranged to be energized through the `said relay in accordance with received signal impulses, and a reactance I element electrically connected to the said lamp foiV storing electric energy to maintain the said lamp illuminated for a longer period than is 4occupied by the signal impulse.

7. In a receiving apparatus for television systems, the combination of a relay operated by the received signals, an electric lamp, an electric supply circuit for the lamp and operated by the said #relay in accordance with received signal impulses, and lan electric condenser connected in shunt Wit the said lamp for maintaining the lamp illuminated over a longer period than is occupied by eachsignal impulse. r Y

8. In receiving apparatus for television the combination of a plurality of illuminating elements one for each unit area of a receiving screen, means for distributing electric energy in accordance with received impulses to each said illuminating element in turn and a reactance uni/tv for each illuminating element electrically connected thereto to store energy when the element is receiving energy due to the signal and to subsequently electrostatically control an electric current to maintain the illumination of the element after it is disconnected from the electric energy.

9. In receiving apparatus for television the combination of a plurality of illuminating elements one for each unit area of a receiving screen, means for distributing electric energy in accordance with received impulses to each said illuminating element in turn, and a condenser for each illuminating element electrically connected in shunt therewith to store energy when the element is receiving energy due to the signal to maintain the illumination of the element after it is disconnected from the electric energy.

l0. A television system comprising an image producing device having a plurality of elements one for each elemental area of a ileld of view, a source of energy for energizing the elements of said image producing device to cause light to be emitted therefrom, means for generating electrical impulses corresponding to the tone values of elemental areas of a field of view for controlling said energization of each element of the image producing device to control the intensity of the light emitted therefrom over a range of intensities between a minimum and a maximum value, thereby producing an image of said eld of view in a variety of tone values between black and white, and means for causing said energization of an element to persist for a period after the controlling electrical impulse for that element is interrupted.

l1. In receiving apparatus employed in the art herein described, the combination of a picture plane divided into elementary areas, each area having its own source of illumination embodying a gaseous lamp, means for transiently .exciting said sources, and means including a condenser and a resistance in circuit with the gaseous lamp for securing persistence of said illumination after the exciting means has passed on.

12. In receiving apparatus employed in the` art herein described, the combination of a picture plane divided into elementary areas, separate means for illuminating each of said areas, including a gaseous lamp, a resistance and a condenser in circuit with the gaseous lamp, and

means for switching an exciting current successively to a plurality of said illuminating means, whereby said elementary areas are successively illuminated and the illumination thereof caused to persist for'a time approximately equal to the persistence of vision of the human eye.

13. An electro-optical image producing system comprising atransmitting station and a receiving station, a transmission medium connecting said stationsmeans including a scanning device at said transmitting station for causing electrical impulses corresponding to the tone values of elemental areas of the eld of view having a variety of tone values between black and white to be impressed on said transmission medium, a bank of electric light elements at said receiving station, one for each elemental area of a field of View, adapted to produce light when current ows therethrough, a source of current at said receiving station for energizing said elements to cause light to be emitted therefrom, means for controlling said energization of the light producing elements in accordance with the electrical impulses received over said transmission medium,

thereby controlling the intensity of the light produced by each element and causing an image to be produced having a variety of tone values between black and white, and means for causing the energization of an element to be maintained for a period after the controlling electrical impulse for that element is interrupted, said period being a large part of the period required to scan said field of view.

14. In an electro-optical image producing system, a bank of light emitting elements each corresponding to an elemental area of a field of View, means for energizing said elements by energy from a local source to cause light to be generated and emitted thereby, means for controlling the energization of said elements in succession and repeatedly one at a time, and means the elemental portions of which are energized under control of said control means in accordance with the instantaneous aspects of corresponding elemental areas of said eld of view for maintaining each light emitting element energized during a cycle of energization of the remaining elements, said control means being capable of causing a decrease in the energization of an elemental portion within an elemental control period if the light tone value of the corresponding elemental area in said eld of view has decreased since the preceding energization readjustment for that elemental portion, or an increase in the energization if the tone value has increased.

15. A television system comprising an image producing device having a bank of electric lamps, a source of energy for exciting said lamps to cause light to be emitted therefrom, means for receiving electrical impulses corresponding to the tone value of elemental areas of the eld of view, means under control of said last-mentioned means for controlling the energization of said lamps in succession and repeatedly one at a time, and means the elemental portions of which are energized under control of said control means for maintaining each lamp energized during a cycle of energization of the remaining lamps, said control means being capable of causing a decrease in the energization of an elemental portion within an elemental control period if the light tone value of the corresponding elemental area of said field of view has decreased since the preceding energization readjustment for that elemental portion, or an increase in the energization if the light tone value has increased.

16. In electro-optical image producing apparatus the combination with an array of elec- 

